The present invention relates to a control system for an infinitely variable transmission, and more particularly relates to an infinitely variable belt-drive transmission with an electromagnetic clutch for transmitting power of an automotive engine to driving wheels of a vehicle.
For the purpose of improving the fuel consumption of the automotive engine, a fuel control system for cutting off fuel during coasting of a vehicle is disclosed in Japanese patent laid open No. 57-131842. The system is such that when an accelerator pedal is not depressed at high vehicle speed higher than a predetermined value, fuel is cut off, and when the accelerator pedal is depressed or the speed decreases below the predetermined value, fuel is supplied, thereby re-starting the engine.
On the other hand, an infinitely variable belt-drive transmission connected to a crankshaft of an engine through an electromagnetic clutch is proposed by applicant. The transmission is provided with a selector device for changing the transmission to forward drive state (D range), reverse drive state (R range) or neutral state (N range). When the N range is selected, clutch current is cut off to disengage the electromagnetic clutch.
In an infinitely variable transmission provided with the above-described fuel cut off system, the system must be so arranged that when the N range is selected from the D range under the fuel cut off state, fuel is supplied to re-start the engine. During the D range driving under the fuel cut off state, the engine is driven by wheels of the coasting vehicle through the transmission system and electromagnetic clutch. In such a condition, when the N range is selected and the electromagnetic clutch is disengaged, engine speed rapidly decreases, because of a small inertial mass of a drive member of the clutch which is connected to the crankshaft of the engine. If the supply of the fuel is delayed upon the selection of the N range, the engine can not be started due to very low engine speed. The belt-drive transmission is provided with pressure oil servo devices for shifting movable conical discs of drive and driven pulleys to keep the belt at proper positions on the pulleys. When the engine stalls, an oil pump for supplying the pressure oil stops, resulting in a decrease of the pressure of the pressure oil. Accordingly, the movable conical discs fail to hold the belt, so that the belt slips on the pulleys, which will cause breakdown of the transmission.